Micro-electrodes are used for the electrochemical detection of various parameters of a substance. For example, a micro-electrode may be used to detect, or measure the concentration of, a particular compound in a test substance. Typically, micro-electrodes contain an electrode which has at least one dimension which is equal to or less than 50 μm, and frequently a dimension of from 1 to 25 μm. The use of these systems as sampling devices brings a number of potential benefits including speed of operation, accuracy and minimal sample requirement.
The common forms of large scale production fabricated micro-electrodes are either micro-disc, micro-band or interdigitated electrodes. A micro-disc electrode is a plate like electrode with a diameter of less than about 25 μm whereas the micro-band electrode consists of a stripe with a thickness or smallest dimension of less than about 25 μm. The interdigitated electrode has a more complex form of two combs with their teeth inter meshed.
By using these micro-electrodes in conjunction with enzymes or other electro-active substances it is possible to create sensors that provide quantitative measurement of target parameters through reactions with the corresponding electro-active substance.
However, several problems occur when using the micro-electrodes known in the art in conjunction with an electro-active substance. Firstly, difficulties are frequently experienced in fixing the electro-active substance to the electrodes and movement of the substance away from its desired location is often seen. Systems containing several micro-electrodes on a single substrate are particularly susceptible to problems in this regard, since enzymes which are not sufficiently attached to their electrode become loose and migrate from one sensor to another causing cross-contamination. This type of problem is exacerbated by the effect of the sample flowing over the micro-electrode, which tends to wash the electro-active substance off the electrode.
A common manner of immobilizing the electro-active substance, at least to some extent, is to dry it in position on the electrode. However, this is typically not sufficient to hold the electro-active substance in place. Furthermore, drying the electro-active substance on top of the micro-electrode can cause electrical fouling of the electrode.
It is therefore an object of the present invention to provide a micro-electrode which is capable of holding an electro-active substance at the electrode ready for sample testing and which will restrict movement of any such electro-active substance whilst the sample flows over the micro-electrode. It is also desired that the problems of electrode fouling which occur when an electro-active substance is dried to the electrodes will be avoided or reduced.